In concrete engineering, water reducers are key admixtures to improve workability, strength and durability. However, the mineral composition, fineness and hydration characteristics of different concrete vary greatly. If the water reducer is not selected properly, it may lead to poor concrete fluidity, rapid slump loss, and even strength loss. Therefore, during the construction process, it is necessary to select a suitable water reducer according to the type of cement.
Common Concrete Types and Characteristics
>> Ordinary strength concrete
Strength range: C15~C30, compressive strength of 15~30 MPa.
Conventional ratio: cement, sand, gravel and water.
Applications: house construction, road base, small components, etc.
Features: low cost, simple construction, but average durability.
>> High-Strength Concrete HSC
Strength range: C50~C100, compressive strength of 50~100 MPa.
Features: Silica fume, high-efficiency water reducer, low water-cement ratio (≤0.35).
Applications: core tube of high-rise buildings, long-span bridges.
>> Self-compacting concrete SCC
Self-compacting concrete is a highly fluid and stable concrete that can completely fill the formwork and evenly wrap the steel bars without vibration, forming a hardened body with high density.
Ratio: The water-cement ratio is generally 0.28~0.38. Low water-cement ratio can ensure strength, but it needs to be adjusted by water reducer.
Paste volume: Usually 35%~45% of the total volume of concrete, while ordinary concrete is only 28%~32%.
Powder content: The total amount of cement and admixtures is ≥450 kg/m³ to ensure sufficient lubricity.
Applications: Densely reinforced walls, steel tube concrete, prefabricated components, special-shaped structures, tunnel linings, underwater concrete, shielding layers of nuclear power plants with high density requirements, and injection into narrow gaps to reinforce old buildings.
>> Lightweight Concrete
Lightweight concrete refers to a type of concrete with a dry density significantly lower than that of ordinary concrete (usually ≤1950 kg/m³, ordinary concrete is about 2400 kg/m³). It is mainly lightweight by using lightweight aggregates, introducing bubbles or reducing solid materials.
Applications: High-rise buildings that need to reduce their own weight, prefabricated components (lightweight wall panels, floor slabs), roof insulation layers, aerated concrete blocks, bridge projects, offshore platforms, etc.
>> Fiber-Reinforced Concrete FRC
Fiber-reinforced concrete is a composite material that is uniformly mixed with short-cut fibers (such as steel fibers, synthetic fibers, glass fibers, etc.) in the concrete matrix to improve its tensile strength, crack resistance, toughness and durability. The addition of fiber can significantly inhibit the brittle failure of concrete, making it show better ductility and energy absorption capacity when bearing load.
Applications: Industrial floor, tunnel lining, military protection, building decoration, bridge reinforcement.
>> Polymer Concrete
Polymer concrete is a composite material formed by combining organic polymers (such as epoxy resin, unsaturated polyester, acrylate, etc.) with aggregates to completely replace cement as a cementitious material. Compared with traditional cement concrete, it has the characteristics of ultra-high strength, corrosion resistance, fast hardening and early strength, and is widely used in special engineering fields, such as chemical plant floors and sewage pipe repairs.
>> Pervious Concrete
Pervious concrete is a special concrete with a continuous pore structure that allows water to quickly penetrate into the ground and has a certain bearing capacity.
Ratio:
Cement: ordinary portland cement (grade 42.5 or higher), dosage 250~400 kg/m³.
Admixtures: silica fume (5%~10%), fly ash (replaces part of cement to improve durability).
Single-grade coarse aggregate: crushed stone or recycled aggregate is commonly used.
Reinforcement agent: polymer emulsion or fiber to improve crack resistance.
Water reducer: polycarboxylic acid water reducer, reduce water-binder ratio, and reduce slurry blocking pores.
Water-binder ratio (W/B): usually 0.25~0.35, the slurry only wraps the surface of the aggregate and does not fill the voids.
>> Mass Concrete
Mass concrete usually refers to a concrete structure with a minimum size of ≥1 meter, or a concrete structure that is prone to temperature cracks due to the internal and external temperature difference of ＞25℃ caused by hydration heat. The core challenge is to control the temperature stress caused by hydration heat to ensure structural integrity and durability.
Proportion: It is necessary to add a retarding water reducer to delay the temperature peak and an expansion agent to compensate for shrinkage.
Classification of Water Reducers
Water reducers can be divided into the following categories according to their water reduction rate:
(1) Ordinary water reducers (sodium lignosulfonate, molasses series)
Water reduction rate: 5%~10%
Applicable to general concrete, low cost, but rapid slump loss.
(2) High-efficiency water reducers (poly naphthalene sulfonate, melamine series)
Water reduction rate: 12%~20%
Applicable to high-strength concrete, but may cause bleeding or slow setting problems.
(3) High-performance water reducers (Polycarboxylate Superplasticizer PCE)
Water reduction rate: 25%~40%
Good dispersibility, long slump retention time, currently the mainstream choice.
(4) Slow-setting water reducer (sodium gluconate and PCE)
Water reduction rate: 15%-30%
Delays setting, suitable for high-temperature construction.
How to choose the right water reducer according to the concrete type?
| Concrete Type | Water Reducer Type | Key Requirements |
| Ordinary Concrete (C30) | Lignosulfonate or Naphthalene-based | Cost-effectiveness prioritized |
| High-Strength Concrete (C60) | PCE (Polycarboxylate Ether) | Water reduction rate >25% |
| Self-Compacting Concrete SCC | Slump-retaining PCE | Slump flow >650mm |
| Lightweight Concrete | PCE or Naphthalene-based | Control aggregate buoyancy |
| Fiber-Reinforced Concrete | PCE + Steel fiber-specific formulation | Fiber dispersion |
| High-temperature Construction | Retarded PCE or Naphthalene-glucose compound | Initial setting time extended to 4-6h |
Common problems and solutions
(1) Slump loss is too fast, the slump rate is greater than 50mm within 30 minutes
Reasons:
High C3A content in cement (> 8%), adsorbing water reducer molecules.
High temperature (> 35℃) accelerates hydration.
Water reducer has poor adaptability to cement.
Solutions:
✅ Use slump-retaining PCE superplasticizer.
✅ Increase the retarding component, add sodium gluconate 0.03%~0.1%.
✅ Reduce the mixing temperature.
(2) Concrete bleeding and segregation
Reasons:
Excessive water reducer (overdosage of more than 0.2%), too low sand ratio (< 38%), insufficient powder material.
Solutions:
✅ Adjust the mix ratio: increase the sand ratio to 40%~45%, or increase the powder content (> 400kg/m³).
✅ Add viscosity enhancer (VMA): such as hydroxypropyl methylcellulose (HPMC), dosage 0.02%~0.05%.
✅ Reduce the amount of water reducing agent: re-test according to the specification.
(3) Setting time is too early or too late
Reasons:
Early setting: high content of hemihydrate gypsum in cement, or misuse of early strength water reducing agent.
Retarded setting: excessive retarder or low temperature environment.
Solutions:
✅ Early setting treatment: temporary remedy with retarder (such as sodium citrate).
✅ Check the SO₃content of cement.
✅ Retarded setting treatment:
✅ Rising temperature curing, use early strength water reducing agent instead.
(4) Strength does not meet the standard
Reasons:
Water reducing agent contains excessive air entraining components, water-cement ratio is not effectively reduced, and curing is improper.
Solutions:
✅ Compound defoaming agent (such as silicone, control air content 3%~5%).
✅ Verify water reduction rate: pass the net slurry fluidity test.
✅ Strengthen curing: cover with film to keep moist for more than 7 days.
(5) Pipe blockage during pumping, loss of fluidity
Reasons:
Insufficient collapse protection of water reducer, too long pipe or too many elbows, poor aggregate shape.
Solutions:
✅ Use high collapse protection PCE water reducer.
✅ Optimize pumping process: apply lubricant to the inner wall of the pipe.
✅ Control aggregate quality: needle-like content <10%.
(6) Too many bubbles on the concrete surface
Reasons:
The air entrainment of water reducer is too strong, insufficient or excessive vibration.
Solutions:
✅ Adjust water reducer: switch to low air entrainment PCE water reducer.
✅ Optimize vibration: insert vibration for 20~30 seconds per point.
✅ Formwork treatment: apply defoaming release agent.
(7) Water reducer fails in winter construction, slow condensation at low temperature
Reasons:
The low temperature activity of water reducer is reduced, and the cement hydration rate is reduced.
Solutions:
✅ Use antifreeze water reducer (containing sodium nitrite component).
✅ Heating raw materials: water temperature to 40~60℃, aggregate＞5℃.
✅ Composite early strength agent: add CaCl2.
(8) Over-addition of water reducer leads to segregation, severe bleeding of concrete, and significant reduction in strength.
Solutions:
✅ Emergency remedy: add additional cement (5%~10%) and stir quickly.
✅ Strict measurement: use automatic feeding system (error <±1%).